Process

ABSTRACT

The invention relates to a process for converting 1-phenylethanol into styrene, which process involves:
         (1) contacting a feed containing 1-phenylethanol, organic acid and 2-phenylethanol with a catalyst to obtain a product containing styrene, and   (2) removing ester compounds based on 2-phenylethanol and organic acid from the product of step (1),
           in which process the feed of step (1) has a molar ratio of organic acid to 2-phenylethanol of at least 1:10.

FIELD OF THE INVENTION

The present invention relates to a process in which feed comprising1-phenylethanol (also known as α-phenylethanol or methyl phenylcarbinol) is contacted with catalyst.

BACKGROUND OF THE INVENTION

A commonly known process comprises the manufacture of styrene andpropylene oxide starting from ethylbenzene and propene. In general suchprocess involves the steps of (i) reacting ethylbenzene with oxygen orair to form ethylbenzene hydroperoxide, (ii) reacting the ethylbenzenehydroperoxide thus obtained with propene in the presence of anepoxidation catalyst to yield propylene oxide and 1-phenylethanol, and(iii) converting the 1-phenylethanol into styrene by dehydration using asuitable dehydration catalyst.

As described in U.S. Pat. No. 4,400,558, oxidation of ethylbenzene givesby-products such as 1-phenylethanol and acetophenone, and in minoramounts 2-phenylethanol and its precursors, such as 2-phenylethylhydroperoxide. In step (ii) ethylbenzene hydroperoxide is itselfconverted to 1-phenylethanol, while more acetophenone and2-phenylethanol are formed as by-products. Propene, ethylbenzene andpropylene oxide are usually removed from the reaction mixture of step(ii) by distillation. The residue comprises 1-phenylethanol,acetophenone and a variety of by-products including 2-phenylethanol.This residue is subjected to step (iii). Styrene and acetophenone areusually removed from the reaction mixture obtained in step (iii), andthe reaction mixture obtained can be recycled and sent again to thedehydration unit. The acetophenone rich fraction is generallyhydrogenated to convert acetophenone to 1-phenylethanol, which can alsobe sent to the dehydration unit.

A problem of 2-phenylethanol is that it is less easily converted intostyrene while it cannot easily be separated from 1-phenylethanol bydistillation. This means that 2-phenylethanol tends to build up in thedehydration unit.

SUMMARY OF THE INVENTION

It has now been found that 2-phenylethanol can be removed in a simpleand effective way. It was found that 2-phenylethanol reacts more readilythan 1-phenylethanol with organic acids such as benzoic acid in thedehydration unit. Organic acids can be added to the reaction mixturecomprising 1-phenylethanol and 2-phenylethanol. However, generallyorganic acids are produced in the preparation of ethylbenzenehydroperoxide and/or propylene oxide. Therefore, the propylene oxidemanufacturing process can be simplified in a further aspect in thatorganic acids do not need to be removed or need to be removed to alesser extent in the process preceding the dehydration unit.

Therefore, the present invention now relates to a process for converting1-phenylethanol into styrene, which process comprises:

-   -   (1) contacting a feed comprising 1-phenylethanol, organic acid        and 2-phenylethanol with a catalyst to obtain a product        comprising styrene, and    -   (2) removing ester compounds based on 2-phenylethanol and        organic acid from the product of step (1),        -   in which process the feed of step (1) has a molar ratio of            organic acid to 2-phenylethanol of at least 1:10.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, ethylbenzene, 1-phenyl-ethanol,2-phenylethanol and styrene can contain substituents. The substituentszeal be either on the phenyl ring or on the ethyl or ethanol or ethylenechain. Most specifically, the compounds are unsubstituted ethylbenzene,1-phenylethanol, 2-phenylethanol and styrene.

The feed comprising 1-phenylethanol, organic acid and 2-phenylethanolfor use in the present process will generally have been obtained by aprocess comprising:

-   -   (a) oxidation of ethylbenzene to obtain a reaction product        containing ethylbenzene hydroperoxide    -   (b) optionally washing the reaction product of step (a),    -   (c) reacting at least part of the reaction product containing        ethylbenzene hydroperoxide with propene to yield propylene oxide        and aryl alcohol, and    -   (d) removing propylene oxide from the product obtained in step        (c).

The product of step (d) can suitably be used as feed for step (1) of theprocess according to the present invention.

Conventionally, the above process for manufacturing the feed comprising1-phenylethanol would comprise washing the reaction product of step (a)with aqueous base in an amount sufficient to neutralize acidiccomponents thereof and separating the resulting mixture into an aqueousstream and a deacidified organic stream. The base contaminated,deacidified hydroperoxide stream would subsequently be washed with waterand the resulting mixture separated into an organics contaminated waterphase and an organic phase having a reduced alkali metal content. Suchprocess has been described in U.S. Pat. No. 5,883,268 hereinincorporated by reference. Recently, it has been found that it can bebeneficial not to wash the reaction product containing hydroperoxidewith aqueous base. This has been described in co-pending European patentapplication 02250791.7 (our case TS 1212). However, the present processmakes even the water wash obsolete. Therefore, in the present inventionthe reaction product containing ethylbenzene hydroperoxide is preferablyused without having been washed with water or aqueous base.

The reaction product containing ethylbenzene hydroperoxide obtained byoxidation of an ethylbenzene compound, generally contains organic acids.These organic acids generally comprise a substantial amount of benzoicacid and smaller amounts of other acids. It has been found to beacceptable that these organic acids are present during the epoxidationstep wherein ethylbenzene hydroperoxide is reacted with propene to yieldpropylene oxide and 1-phenylethanol. If the organic acids remain in thereaction mixture during epoxidation, they can be put to good use in thesubsequent step where they can react with 2-phenylethanol.

Ethylbenzene hydroperoxide is reacted with propene to yield propyleneoxide and 1-phenylethanol. In such epoxidation step a homogeneouscatalyst or a heterogeneous catalyst can be applied. Molybdenumcompounds are frequently applied as homogeneous catalysts, whilecatalysts comprising titanium on a silica carrier are often used asheterogeneous catalysts. Conditions under which epoxidation is carriedout are known in the art and include temperatures of 75° C. to 150° C.and pressures up to 80 bar. The reaction medium is preferably in theliquid phase.

The effluent from the epoxidation step is normally first subjected to aseparation treatment such as distillation to remove the propylene oxideformed. From the residual stream, ethylbenzene is generally removed bydistillation. The residual stream will generally contain1-phenylethanol, acetophenone and 2-phenylethanol. This residual streamwill further contain benzoic acid if the alky aryl hydroperoxide has notbeen washed or washed only to a limited extent.

This residual stream can be subjected to one or more further separationtreatments. Such separation treatment can comprise separating compoundshaving a molecular weight of at least 195 from the aryl alcoholcontaining stream. Such process has been described in European patentapplication 02252618.0 herein incorporated by reference.

As mentioned above, the feed for use in the present invention willcontain both 1-phenylethanol and 2-phenylethanol. Generally, asubstantial amount of 1-phenylethanol will have been produced in thereaction of aryl hydroperoxide with propene, and a much smaller amountof 2-phenylethanol.

The feed for use in step (1) of the present invention will generallycomprise from 60% wt to 85% wt of 1-phenylethanol, of from 0.3% wt to10.0% wt of 2-phenylethanol and of from 0.1% wt to 10.0% wt of organicacid.

The molar ratio of 1-phenylethanol to 2-phenylethanol in step (1) willgenerally be of from 5:1 to 300:1, more specifically of from 20:1 to200:1.

The molar ratio of organic acid to 2-phenylethanol is at least 1:10,more specifically of from 1:5 to 20:1, more specifically of from 1:5 to10:1, more specifically of from 1:5 to 5:1, most specifically of from1:2 to 2:1. Most preferably, the 2-phenylethanol and organic acid arepresent in about equimolar amounts.

The organic acids which can be present depend on the ethylbenzenecompound subjected to oxidation. Generally, the majority of the organicacids present will be benzoic acid.

The ester compound formed will generally be 1-phenylethylbenzoate.

Additional organic acids can be added to the reaction mixture to remove2-phenylethanol. However, it is preferred to produce the organic acidsfor use in the present invention in the manufacture of the feed byprocess steps (a)-(d), more preferably by steps (a), (c) and (d) only.

Step (1) of the present invention comprises dehydration of1-phenylethanol. This process is well known in the art. It can becarried out both in the gas phase and in the liquid phase. Suitabledehydration catalysts include for instance acidic materials likealumina, aluminium silicates, H-type synthetic zeolites, mineral acids,organo-sulphonic acids and carboxylic acids. Dehydration conditions arealso well known and usually include reaction temperatures of 100-260° C.for liquid phase dehydration and 210-320° C., typically 280-310° C., forgas phase dehydration. Pressures usually range from 0.1 bar to 10 bar.In principle, any known dehydration process can be applied in theprocess according to the present invention. For the purpose of thepresent invention, liquid phase dehydration is preferred. It wasobserved that the 2-phenylethanol and organic acid reacted well inliquid phase reaction conditions. In a preferred embodiment, the liquidphase dehydration is carried out at a temperature in the range of from100° C. to 260° C. and a pressure of from 0.1 bar to 1.0 bar using ahomogeneous acid dehydration catalyst, preferably an organo-sulphonicacid catalyst. A preferred catalyst is para toluene sulphonic acid.

Liquid phase dehydration is well known to someone skilled in the art,for example from U.S. Pat. No. 3,526,674 herein incorporated byreference.

A well known phenomenon in the liquid phase dehydration of phenylethanolis the formation of substantial amounts of by-products, such as heavycondensation products. The production of these undesirable productslessens the economics and efficiency of the process. In order to reducethe formation of undesirable heavy by-products, an agent such as nitroor nitrosubstituted aromatics can be added. This has been described inmore detail in U.S. Pat. No. 5,639,928 herein incorporated by reference.

The reaction mixture obtained in step (1) of the present invention willcontain styrene. The ester compounds based on 2-phenylethanol andorganic acid can be removed from the product of step (1) before removingstyrene, or the styrene can be removed from the product of step (2).

The ester compounds can be removed from other compounds relativelyeasily. A suitable method comprises subjecting at least part of theproduct of step (1) to distillation.

Preferably, at least part of the product of step (2) is recycled to step(1) as discussed in more detail hereinafter.

Independent from the removal of the ester compounds, the reactionmixture obtained in step (1) will generally be separated into a styrenerich fraction and a styrene lean fraction. The separation of the styrenerich fraction and the styrene lean fraction can be effected in severalways, but most suitably is achieved by flashing or distillation. In suchseparation, the styrene rich fraction will generally be removed as thetop fraction.

The styrene lean fraction contains compounds such as unconverted1-phenylethanol and acetophenone. The 1-phenylethanol can be recycled tothe dehydration step (1).

An acetophenone rich fraction usually is separated off from the reactionmixture of step (1). This fraction can be hydrogenated to convertacetophenone to 1-phenylethanol, which can be used as feed for step (1).

The styrene rich fraction obtained by the process according to thepresent invention can be purified further in any way known to someoneskilled in the art.

The invention is further illustrated by the following examples withoutrestricting its scope to these particular embodiments.

EXAMPLE 1

In a reactor, air was blown through ethylbenzene. The product containedethylbenzene hydroperoxide.

The product obtained was reacted with propene in the presence of atitanium on silica catalyst as described in the Example according to theteaching of EP-A-345856 herein incorporated by reference. Unconvertedethylbenzene and propylene oxide were removed from the product, and acrude 1-phenylethanol feed was obtained. This feed was subjected to adehydration reaction. Styrene product was removed, and unconverted1-phenylethanol and 2-phenylethanol were recycled to the dehydrationreactor feed. Acetophenone from the dehydration reaction product waspartially hydrogenated to 1-phenylethanol and also recycled to thedehydration reactor feed. The combined feed stream to the dehydrationreactor (referred to below as “Feed A”) contained the followingcompounds:

1-phenylethanol 76.7% wt 2-phenylethanol  2.5% wt benzoic acid 0.13% wtacetophenone 13.1% wt

The remainder of the feed consisted of a wide range of furthercompounds. No substantial amount of further acids was present.

Benzoic acid was added to this feed so that the total benzoic acidconcentration was 1.1% w.

The feed containing 1.1% w benzoic acid was subjected to dehydrationreaction in the liquid phase, as follows: para toluene sulphonic acidwas added to the feed at a level of 200 ppmw. The feed containingcatalyst was fed at a rate of 30 grams/hour to a reactor containing 64 gof heavy liquid formed in a previous dehydration reaction. The reactorwas operated at 220° C. and 0.2 bar in once through mode. Vapor productswere allowed to exit the reactor via a distillation column comprising 5trays, to which reflux was applied. Overhead products were condensedinto an organic layer and an aqueous layer. The organic layer wasanalyzed using gas chromatography to determine styrene, 1-phenylethanoland 2-phenylethanol concentrations. Heavy components formed were allowedto accumulate in the reactor. The reactor was operated continuously for48 hours. At the end of the run, the amount of heavy components formedwas determined by weighing. The heavy liquid was also analyzed by gaschromatography to determine the concentrations of the ester of2-phenylethanol with benzoic acid, and the ester of 1-phenylethanol withbenzoic acid.

During the run a total of 35 g of 2-phenylethanol was fed to thereactor. Of these, 16 g (45%) was recovered in overhead product.Therefore, 19 grams (55%) of the 2-phenylethanol remained in the reactoror reacted to other compounds in the reactor, and would not lead tobuild-up of 2-phenylethanol in a recycle. Of these, 12 grams was foundto have reacted to form the ester of 2-phenylethanol and benzoic acidwhich was present in the reactor (23 grams of ester present). The esterof 1-phenylethanol and benzoic acid could not be detected in the heavyliquid.

COMPARATIVE EXAMPLE

The above example was repeated with the exception that no additionalbenzoic acid was added to “Feed A”. The reaction was continued for atotal of 67 h. During the run a total of 50 g of 2-phenylethanol was fedto the reactor. Of these, 36 g (72%) were recovered in overhead product.Therefore, only 14 grams (28%) of the 2-phenylethanol remained in thereactor or reacted to other compounds in the reactor and would not leadto build-up of 2-phenylethanol in a recycle. Of these, 3 grams was foundto have reacted to form the ester of 2-phenylethanol and benzoic acidwhich was present in the reactor (6 grams of ester present). The esterof 1-phenylethanol and benzoic acid could not be detected in the heavyliquid.

1. A process for converting 1-phenylethanol into styrene comprising: (1)contacting a feed comprising 1-phenylethanol, organic acid and2-phenylethanol with a catalyst to obtain a product comprising styrene;and, (2) removing ester compounds based on 2-phenylethanol and organicacid from the product of step (1); wherein the feed of step (1) has amolar ratio of organic acid to 2-phenylethanol of at least 1:10.
 2. Theprocess of claim 1, in which step (1) is carried out in the liquidphase.
 3. The process of claim 2, in which the feed of step (1) has amolar ratio of organic acid to 2-phenylethanol of from 1:5 to 20:1. 4.The process of claim 2, in which the ester compounds based on2-phenylethanol and organic acid are removed by subjecting at least partof the product of step (1) to distillation.
 5. The process of claim 2,in which at least part of the product of step (2) is recycled to step(1).
 6. The process of claim 2, in which ester compounds based on2-phenylethanol and organic acid are removed from the product of step(1) before removing styrene.
 7. The process of claim 2, in which styreneis removed from the product of step (2).
 8. The process of claim 2,wherein the feed comprising 1-phenylethanol, organic acid and2-phenylethanol is obtained by a process comprising: (a) oxidation ofethylbenzene to obtain a reaction product containing ethylbenzenehydroperoxide; (b) washing the reaction product of step (a); (c)reacting at least part of the product of step (b) with propene to yieldpropylene oxide and 1-phenylethanol; and (d) removing propylene oxidefrom the product obtained in step (c).
 9. The process of claim 1, inwhich the feed of step (1) has a molar ratio of organic acid to2-phenylethanol of from 1:5 to 20:1.
 10. The process of claim 1, inwhich the ester compounds based on 2-phenylethanol and organic acid areremoved by subjecting at least part of the product of step (1) todistillation.
 11. The process of claim 1, in which at least part of theproduct of step (2) is recycled to step (1).
 12. The process of claim 1,in which ester compounds based on 2-phenylethanol and organic acid areremoved from the product of step (1) before removing styrene.
 13. Theprocess of claim 1, in which styrene is removed from the product of step(2).
 14. The process of claim 1, wherein the feed comprising1-phenylethanol, organic acid and 2-phenylethanol is obtained by aprocess comprising: (a) oxidation of ethylbenzene to obtain a reactionproduct containing ethylbenzene hydroperoxide; (b) washing the reactionproduct of step (a); (c) reacting at least part of the product of step(b) with propene to yield propylene oxide and 1-phenylethanol; and (d)removing propylene oxide from the product obtained in step (c).
 15. Theprocess of claim 1 in which step (1) is carried out in the liquid phase;the feed of step (1) has a molar ratio of organic acid to2-phenylethanol of from 1:5 to 20:1; the ester compounds based on2-phenylethanol and organic acid are removed by subjecting at least partof the product of step (1) to distillation; at least part of the productof step (2) is recycled to step (1); and styrene is removed from theproduct of step (2).